It has long been known that electronic components assembled into a piece of electronic equipment are susceptible to damage of a number of forms. Physical impact, contact with dust, invasion by water causing corrosion, etc. are all well-known mechanisms by which an electronic circuit may be damaged. It is also known to coat an electronic component or a structure containing many components with a conformal coating of a protective material to guard the component from damage. Typically, these coatings are polymers that are applied to the component, such as a printed circuit board (PCB) for example, by any of a number of processes, including, but not limited to, spraying, layering, dipping, etc. The coating sets up by heating, such as in the case of a thermoset polymer; by reaction of various components, as in the case of an epoxy resin or polyurethane coating; or by the evaporation of a carrier or component, as in the case of a silicone or acrylic polymer.
Once cured, the coating is an intractable solid. The inertness of the coating is desired, of course, to protect the components. However, in the case of complex and/or costly components, it is often desired to fix or replace one or more of the components on an assembly in the case of component failure; component replacement, as in the case of an upgrade of the system; or to make some other engineering modification. This situation frequently happens in the case of PCBs which are assembled with a large number of components, particularly integrated circuits (ICs). The assembled PCB may be valued at hundreds or thousands of dollars. However, the conventional protective coatings work so well that it is very difficult to remove them to make the desired change in the board or component. If it is at all possible to remove the protective coating once in place, it may be accomplished only with hazardous chemicals or processes. Often, even if coating removal is achieved, the PCB and its components may be damaged additionally in the process. Further, these coatings cannot be removed selectively, that is, the entire coating must be removed even if a change is required in only a small part of the board. This characteristic of coating removal subjects the entire board to the possibility of damage, not just during coating removal, but also during the repair or engineering change process since the remainder of the board is exposed.
There is a need in the electronics industry for a protective, conformal coating over electronic components which may be selectively removed to facilitate changes or corrections in the components.